Some switched-mode power converters perform synchronous rectification techniques as a way to boost efficiency of the power converter. With synchronous rectification, diodes (e.g., low-side switches of a half-bridge, secondary-side diodes of a flyback or synchronous rectifier, etc.) are replaced with “synchronous rectifiers” (SR). An example of a typical SR is a metal-oxide-semiconductor field-effect-transistor (MOSFET). While a SR MOSFET may increase the overall efficiency of the power converter by reducing the conduction losses that would otherwise arise if a diode were used, the power converter may experience other types of drawbacks that are attributed to the SR MOSFET.
For example, a SR MOSFET has an inherent output capacitance (Coss) that, when paired with inductive elements or inductive attributes of the power converter (e.g., leakage inductance of a transformer, other parasitic inductances, etc.), forms an LC circuit that tends to oscillate at a natural frequency given by Coss and L whenever the SR MOSFET stops conducting, its drain-source voltage may oscillate without dampening.
Accordingly, rather than select a SR MOSFET that meets the normal operating parameters of the power converter, the power converter may have to rely on a SR MOSFET that has a voltage rating that is sufficient to withstand a peak voltage associated with a potential oscillation. Such a SR MOSFET may have a higher cost and greater on-resistance RDS-ON which may reduce the efficiency of the power converter. In addition, the voltage oscillations may generates noise, such as electromagnetic interference (EMI), which may lead to other challenges and increased cost associated with the power converter.
Some power converters may include a resistive-capacitive (RC) snubber circuit to dampen and prevent voltage oscillations. However, the introduction of the RC snubber circuit may cause energy to be lost during switching operations of the SR MOSFET which may prevent the power converter from achieving its otherwise maximum potential efficiency.